Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles (2018)

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1 Critical issues associated with connected vehicles and automated vehicles will be faced by state and local transportation agencies and AASHTO. To identify these issues, conduct research to address them, and conduct related technology transfer and information exchange activities, NCHRP initiated Project 20-102, “Impacts of Connected Vehicles and Automated Vehicles on State and Local Transportation Agencies.” NCHRP Research Report 891 presents the specific research and findings of NCHRP 20-102, Task Order 8, “Dedicating Lanes for Priority or Exclusive Use by CVs and AVs.” The overall objective of this task was to develop guidance on identifying and describ- ing conditions amenable to dedicating lanes for connected and automated vehicle (CAV) users. The project team conducted simulation-based analysis of two CAV applications, namely Cooperative Adaptive Cruise Control (CACC) and Dynamic Speed Harmonization (DSH), using two case study sites. The modeling and simulation activity helped the project team in identifying parameters that are sensitive to dedicating lanes to CAV users as well as identifying expected impacts under various conditions of lane dedication, market penetra- tion, demand conditions, combined deployment of applications, and so forth, using virtual computer-based models. The research was done in five steps. Each step is described briefly in this summary. Identify Categories of Benefits and Disbenefits The project team started with a comprehensive literature review identifying the types of stakeholders who benefit (or do not benefit) from dedicated lanes to CAVs, factors influenc- ing these benefits, and the potential performance measures. Specifically, the team identified three types of stakeholders: • Dedicated lane (DL) users, • General purpose lane (GPL) users, and • The owners and operators of the facility. The research team also identified the following factors as influencing the benefits and disbenefits to these stakeholders: • CAV market penetration, representing the percentage of vehicles in the traffic mix with CAV capabilities; • Roadway geometry, including access/egress features, lane attributes, number of lanes, and so forth; • Enforcement intensity, which restricts unallowable categories of users to enter the DLs; • Toll collection attributes, such as whether non-CAV vehicles can use the DLs for a fee; • Operation hours, such as dynamic operations or peak-hour operations; S U M M A R Y Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles

2 Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles • CAV technology, which represents the type of applications allowed on vehicles using these lanes; and • Functional types, which dictate the type of vehicles allowed on the DLs. The literature review also enabled the researchers to document performance measures specific to mobility, energy and environment, safety, and societal benefits that might be achieved by users and non-users of such DLs. Evaluate Existing Modeling and Analytical Frameworks Several CAV applications exist in the research industry today, and assessing all of them was beyond the scope of this study. Accordingly, the project team implemented a selection process to evaluate which applications to consider in this project and which algorithm or modeling framework to use in evaluating these applications. Among the 17 available CAV applications, down-selection considered three criteria: (1) suitability to dedicating lanes, (2) suitability to the CAV environment, and (3) adaptability to simulation models. Two CAV applications, CACC and DSH, were selected for use in this project. The project team utilized modeling and simulation-based analysis to evaluate poten- tial benefits and parameter sensitivity of CAV applications on overall traffic efficiency and safety. Six modeling frameworks were evaluated for CACC modeling, and eight modeling frameworks were evaluated for DSH modeling to identify appropriate algorithms for use in this project. As a result, the team selected the CACC model by Lee et al. (2014) and the DSH model by Ma et al. (2016). Both models were developed for the PTV Vissim microsimula- tion tool; for this study, they were modified to be integrated into a unified programming interface so that they could work together or in isolation. Identify Diverse Case Study Sites Suitable for Evaluation The CACC and DSH models were applied to case study sites that represented real-world transportation networks. To support this, the project team evaluated and ranked nine mod- eling-based test sites to which the team had access. The case study sites were evaluated with regard to: • Overall characteristics (e.g., geography, operational conditions, modes, managed lanes); • Managed lane characteristics (e.g., geometry, allowed users, operating rules, access point configurations); and • The feasibility of modeling CAV applications. Based on the evaluation, the team selected two case study sites: the I-66 corridor in North- ern Virginia and the US-101 corridor in San Mateo County, California. Select, Adapt, and Apply the Evaluation Approach The next task included development of case-study models to conduct simulation-based analysis of CAV applications to evaluate their impacts on DL scenarios under different sen- sitivity parameters. The project team conducted a four-step process to develop and utilize the models to conduct the simulation-based analysis: (1) develop baseline models, (2) inte- grate CAV application models, (3) develop scenarios for the simulation-based assessment, and (4) measure the performance of the applications. Development of the baseline models involved calibration of Vissim-based models to rep- resent real-world operational conditions and certain hypothetical operational conditions.

Summary 3 Integration of CAV application models involved development of CACC and DSH models to work within Vissim’s application programming interface, along with conducting prelimi- nary testing to compare and calibrate the vehicle behavior to field data. Based on the fol- lowing six research issues, the research team then developed a list of scenarios that provided precedence to develop DL guidance for agencies: 1. Impact of priority lane use, with CAVs permitted on high-occupancy vehicle (HOV) lanes, versus exclusive lane use, with CAVs having exclusive access to DLs; 2. Impact of market penetration rates (MPRs), assessed under both DL and non-DL scenarios; 3. Impact of a combination of CAV applications; 4. Impact of varying demand and changing operational conditions on the CAV DL benefits; 5. Impact of access restrictions to the DL under exclusive CAV lane situations; and 6. Impact of hypothetical scenarios such as an incident-related lane closure or moving bottlenecks. For each scenario, the project team performed simulations and captured safety, mobility, and energy/environmental performance measures. Through post-processing of mobility performance measures, societal/equity performance measures also were captured to deter- mine whether, and by how much, DL users received benefits at the expense of GPL users. Identify Typical Laws and Regulations In addition to conducting an operational analysis based on modeling and simulation, the project team conducted a literature review to identify the laws and regulations regarding dedicating lanes to specific categories of users. The review found that, historically, lanes have been dedicated to HOVs, motorcycles and bicycles, buses, alternative fuel vehicles, and trucks. The team also identified the current state of regulatory and legislative affairs with respect to CAVs, and barriers to dedicating lanes for exclusive use by CAVs. Summary of Guidance Based on the findings from the previous tasks, the project team developed specific guid- ance for agencies on operational characteristics and impacts of dedicating lanes to priority or exclusive use by CAVs, as well as regulatory and policy guidance for states and local agencies regarding conditions amenable to dedicating lanes to CAVs. As summarized in the following list of statements, this guidance must be used in conjunction with the type of analysis that went into developing these statements. Scenarios may occur that fall outside of the scope of the analysis conducted in this study, which could potentially enhance or change this guidance. 1. For CACC-DLs, it is advisable to have shared DLs with HOVs at lower market penetra- tion (10%), exclusive DLs at medium market penetration (20 to 45%), and no DLs for higher market penetration (greater than 50%). 2. For lower market penetration of CACC: a. Under shared DL conditions, there may be slight mobility benefits for both DL users and GPL users. b. Under exclusive DL conditions, there may be significant mobility and energy/ environmental benefits to DL uses, at the expense of GPL users. 3. For higher market penetration of CACC: a. Under exclusive DL conditions, there may be moderate to significant mobility and energy/environmental benefits to DL users, and slight to moderate benefits to GPL users.

4 Dedicating Lanes for Priority or Exclusive Use by Connected and Automated Vehicles 4. For lower market penetration of DSH: a. Under shared DL conditions, there may be slight safety benefits for both DL and GPL users. b. Under exclusive DL conditions, there may be slight safety benefits for DL users and significant safety benefits for GPL users (at the expense of their mobility performance). 5. For higher market penetration of DSH: a. Under exclusive DL conditions, there may be moderate to significant improvement in safety and slight improvement in energy/environmental performance for DL users; GPL users would remain unaffected. 6. Combining DSH-enabled vehicles with CACC-enabled vehicles will improve safety, in addition to mobility and energy/environmental performance. 7. CACC DLs can especially provide mobility benefits (in terms of throughput improve- ment), when the corridor is subject to peak or higher-than-peak demand. 8. Mobility benefits are more when there is continuous access to the DLs because even vehicles taking shorter trips can utilize the DLs. 9. Speed differential between DLs and GPLs increases with restricted access to DLs. DLs with exclusive access for CAVs will have a much higher travel speed than GPLs. 10. Average travel speed on GPLs reduces significantly when there is restricted access to DLs. This is because the demand on GPLs will be higher when compared to continuous access, as vehicles taking shorter trips cannot use the DLs. 11. Lane friction (speed differential between DL and adjacent GPL) guidance that warrants when to have barrier separated lanes: a. High market penetration of CAV with shared DLs with HOV demonstrated the lowest lane friction, and does not warrant lane separation barriers or restricted lane access. b. Low market penetration of CAV with shared DLs with HOV also demonstrated relatively lower lane friction. c. High market penetration of CAV with exclusive DLs showed medium lane friction, where the average speeds of the DL and the adjacent GPL differed by 10 to 15 miles per hour (mph). According to Best Practices: Separation Devices between Toll Lanes and Free Lanes, this does not warrant physical separators, but rather buffer-separated double solid lines. d. Low market penetration of CAV with exclusive DLs showed the highest lane friction, on the order of 30 mph. This warrants the need for physical separation for enforce- ment purposes as well as for safety purposes. Additional guidance, along with more-detailed narratives, are provided in the chapter copy.